Effects of D″ anisotropy on seismic velocity models of the outermost core

We explore effects of shear wave anisotropy in D″ on seismic waves utilized in constructing models of the outermost core. Reflectivity synthetic seismograms approximating transverse isotropy (TI) in D″ yield absolute and differential time perturbations of S , SKS , and SKKS of up to several seconds, especially if laterally varying anisotropy is considered. Several studies have used anomalies of this magnitude to infer a 0.5–2.5% P velocity reduction in the outermost 50–150 km of the core, suggesting a stably stratified layer just beneath the core‐mantle boundary. Our data samples the mantle and core beneath Alaska and northern Pacific, a region with strong lateral variations in D″ anisotropy. TI models that predict the magnitude of shear wave splitting seen in the data can account for much (but not all) of the anomalies that isotropic models attribute to outermost core velocity reductions. Future outermost core seismic studies should address such D″ anisotropy effects.